The main reason is google used its piles of cash to push their browser. The side reason is firefox made counterproductive and unnecessary changes: removing the

The main reason is google used its piles of cash to push their browser. The side reason is firefox made counterproductive and unnecessary changes: removing the status bar, australis UI, removing the ability to disable script, dropping alsa support and many other useful features removed proving that user have no freedom of choice and no say. While adding unwanted things (DRM, pocket, hello, etc.) and not fixing broken things. Some power users and long supporter would have sticked with firefox despite google's marketing, had it not piled bad move after bad move and not listening to its users.